JPH04155989A - Manufacture of laminate plated with metallic foil - Google Patents

Abstract

PURPOSE:To reduce the residual strain of a laminate after press formation by putting the thermal expansion coefficient of a mold plate to specified times the laminate, and repeating depressurization and pressurization just before cooling a press hot platen, and again, repeating the depressurization and pressurization with the laminate temperature in specified range. CONSTITUTION:The residual strain is reduced positively making use of the thermal coefficient difference between a laminate and a mold plate. That is, since the residual strain is tensile strain, the thermal expansion coefficient of the mold plate is made larger than that (toward inside of the surface) of the laminate, whereby compressive stress is given toward inside of the surface to remove the residual stress. It is to be desired that the thermal expansion coefficient of the mold plate at this time should be one and a half times to three times that of the laminate. Moreover, depressurization and pressurization are repeated just before the cooling process to make the tensile strength arising in the heating process zero. Furthermore, the depressurization and the pressurization are repeated between 110 deg.C-140 deg.C. It is to make the compressive stress, which has arisen in the laminate by the thermal expansion coefficient between the mold plate and the laminate, zero again while it leads to 11O deg.C-140 deg.C after start of cooling.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for manufacturing a metal foil-clad laminate used for printed wiring boards.

<Conventional technology> Metal foil-clad laminates used for printed wiring boards are heated,
In the circuit board manufacturing process, which involves pressure pressing and repeated heating and humidification, warping and dimensional changes occur in the board, often causing problems during circuit manufacturing work or component assembly work.

On the other hand, in recent years, as boards have become larger, circuits have become more dense, and processing processes have become more automated, requirements for preventing board warpage and dimensional changes have become increasingly strict.

The cause of this warping and dimensional change is often caused by the heating and pressing process. In other words, the laminate is affected by the flow of the resin impregnated into the base material, uncured resin, curing shrinkage, difference in thermal expansion coefficient between the metal foil and the laminate, and difference in thermal expansion coefficient between the stainless steel mold plate and other factors. Residual strain accumulates in the internal in-plane direction, causing warping and dimensional changes when removed from the press or subjected to thermal history during the wiring board manufacturing process.

Therefore, conventionally, as a method for keeping the residual strain low in the pressing process, a depressurizing molding method is used in which the pressure is removed when moving from the heating process to the cooling process.

As a result, in the method of cooling while pressurized without releasing the pressure, the residual strain of the laminate after press forming is 2 to 5 x 10
-', whereas in the decompression molding method, it is reduced to about lXl0-'. This is because the residual strain is released by releasing the pressure.

<Problems to be Solved by the Invention> However, in the conventional decompression molding method as described above, residual strain does not completely disappear and remains to some extent.

This is because the heating plate is not completely opened in a depressurized state, but some pressure is applied to bring the laminate into contact with the heating plate so that heat can be easily removed from the laminate during cooling. This is because there is a binding force.

By the way, there are strict requirements to prevent warpage and dimensional changes, and the recent required value is 0.01% or less in terms of dimensional change rate, whereas the above decompression molding method has a residual strain of about 1X10-' (
0.01%), and the dimensional change rate is 0.0
1% chance of occurrence. This is just below the required value.

This invention was made in view of the above-mentioned conventional problems, and its purpose is to further reduce the residual strain of the laminate after press forming, and to produce metal foil-clad laminates with small warpage and dimensional changes. The object of the present invention is to provide a method for manufacturing a board.

Means for Solving the Problems> In order to achieve the above object, the present invention stacks a predetermined number of semi-cured prepregs made by impregnating a base material with a thermosetting resin, and also coats one or both surfaces with metal. A method for manufacturing a metal foil-clad laminate in which a foil is provided, sandwiched between mold plates, and heated and pressed with a press, wherein the mold plate has a thermal expansion coefficient of 1.5 to 3 times that of the metal foil-clad laminate, and It is characterized by repeating depressurization and pressurization immediately before cooling the press hot platen, and repeating depressurization and pressurization again when the laminated plate temperature is between 110°C and 140°C.

Effect> Residual strain in the in-plane direction generated by press forming is tensile strain, and in the conventional decompression forming method, the residual strain was naturally eliminated by decompressing at the start of cooling, but in the present invention, the residual strain in the laminate is The residual strain is actively eliminated by utilizing the difference in thermal expansion coefficient between the mold plate and the mold plate.

In other words, since residual strain is tensile strain, the coefficient of thermal expansion of the mold plate is made larger than the coefficient of thermal expansion of the laminate (in the in-plane direction), compressive stress is applied in the in-plane direction of the laminate, and the residual strain is eliminated. I did it like that.

The coefficient of thermal expansion of the mold plate at this time is 1 that of the laminate plate.
．． It is preferable to increase the amount by 5 to 3 times. The material of the mold plate may be any material within the above range, and for example, aluminum alloy is suitable.

Further, the reason why the depressurization and pressurization are repeated immediately before the cooling process is to zero out the tensile stress generated in the laminate due to the difference in thermal expansion coefficient between the mold plate and the laminate during the heating process.

Although the number of repetitions of depressurization and pressurization is arbitrary, it is most preferable to perform the depressurization and pressurization only once from the viewpoint of workability.

Furthermore, depressurization and pressurization are repeated between 110°C and 140°C from the start of cooling until the temperature reaches 110°C to 140°C.
This is to reduce the compressive stress generated in the laminate to zero again due to the difference in thermal expansion coefficient between the mold plate and the laminate. If pressurization is continued until the end of the cooling process, the compressive stress generated in the laminate becomes too large, so it is necessary to release the -degree stress. The number of repetitions of depressurization and pressurization is arbitrary, but from the viewpoint of workability, it is most preferable to repeat the depressurization and pressurization only once.

In the heating process, it is desirable that the pressure applied between 50 and -100°C after the start of temperature rise be higher than the pressure applied after 50 to 100°C. This is because until the semi-hardened resin in the prepregs starts to flow, the prepregs are only stacked on top of each other and are not in contact with each other, so it is better to apply as high a pressure as possible to increase the contact area between the prepregs. This is because the temperature increases as the temperature increases and the thermal resistance decreases.

Further, in the present invention, since pressure is applied even during the cooling process, the cooling rate is faster and the press cycle is shorter than that in the decompression molding method.

<Example> The present invention will be explained in detail below.

Glass cloth was used as the base material, epoxy resin was used as the thermosetting resin, and copper foil was used as the metal foil. Eight sheets of prepreg were laminated, and copper foil was placed on both sides.

An aluminum alloy with a thermal expansion coefficient of 2.4 x 10-5/"C was used for the mold plate (the thermal expansion coefficient of a laminate without copper foil is 1.2 x 10-5/"C).

The drawings show a time schedule regarding pressure and temperature during press molding in this example.

As shown in the drawing, the pressure P is 60 kg f 7 cm'' until the laminate temperature T reaches 60°C, and thereafter it is 4 cm.
It was set to 0 kgf/cm2.

In addition, depressurization and pressurization were performed once immediately before cooling start Q1 and at point Q2 when the laminate temperature reached 120° C. during the cooling process (indicated by A and B in the drawing).

As a comparative example, stainless steel was used for the mold plate, and a continuous molding method in which the pressure was kept constant at 40 kgf/cm2 during press molding, and a decompression molding method in which the pressure was released to 3 kgf/cm2 at the start of cooling were performed. .

As a result, the residual strain in the in-plane direction of the laminate after press forming was 0.5 x 10-4 in the manufacturing method according to the present invention, whereas it was 3 x 10-4 in the continuous forming method, and The molding method was 1X10-'.

<Effects of the Invention> As explained above, according to the present invention, the residual strain of the laminate after press forming can be reduced, and a metal foil-clad laminate with excellent warpage characteristics and dimensional stability can be obtained. It has this effect.

[Brief explanation of drawings]

The drawing is an explanatory diagram of a time schedule regarding pressure and temperature during press molding. T... Laminate temperature P... Pressure saw j

Claims (5)

[Claims] 1. A metal foil-clad laminate in which a predetermined number of prepregs made by impregnating base material A with thermosetting resin to a semi-cured state are stacked, metal foil is provided on one or both sides of the prepreg, and the prepregs are sandwiched between mold plates and heated and pressed using a press. In the manufacturing method of
3 times the pressure, and immediately before cooling the press platen, remove the pressure.
A method for manufacturing a metal foil-clad laminate, which comprises repeating pressurization, and repeating depressurization and pressurization again when the laminate temperature is between 110°C and 140°C. 2. 2. The method for manufacturing a metal foil-clad laminate according to claim 1, wherein the mold plate is made of an aluminum alloy. 3. 50 to 10 from the start of temperature rise when heating and pressurizing with a press
2. The method for manufacturing a metal foil-clad laminate according to claim 1, wherein the pressure applied before 0°C is higher than the pressure applied after 50 to 100°C. 4. The number of times of depressurization and pressurization immediately before cooling the press hot plate is 1.
2. The method for manufacturing a metal foil-clad laminate according to claim 1, wherein the method comprises: 5. 2. The method of manufacturing a metal foil-clad laminate according to claim 1, wherein the number of times of depressurization and pressurization is one time when the laminate temperature is between 110 DEG C. and 140 DEG C.